Wind turbines are the largest wind-operated machines to date. Because of the complexity of these great machines and their dependence on consistent, strong wind, turbines are never constructed simply because someone wills it; there must be a power demand to warrant their construction. After years of research and planning, turbines are built to supplement an existing power grid.
Like their wind engine predecessors, turbines components and spare parts can be mass produced. Specially designed facilities have been constructed to accommodate the oversized turbine parts. Because the United States is among the latest nations to utilize wind power, nearly all of the utility-scale wind turbines are manufactured in Europe or Asia by companies that have been in the business for decades.
Initial shipments of turbines to the United States were slowed by a lack of equipment. Only a handful of ports had the proper lifting equipment installed for unloading the large turbine components. Over the years, more ports have been fit to accommodate turbines shipments, and because of the increasing demand for spare turbine parts, some manufacturers have opened new plants and warehouses in the United States.
The tower determines the height of the turbine. The first turbines, like wind engines, were mounted atop open lattice-framed towers available in different heights. Over the years, as turbines became larger in diameter, the lattice frames were replaced by cylindrical steel towers that are fabricated in sections (they have to be, else they would be too large to ship!). These tower sections can be bolted together to achieve the proper height.
The tower contains no operating machinery of any kind. In fact, the inside of a modern wind turbine tower is hollow aside from cables (to bring power to the controllers within the nacelle and to run generated electricity from the nacelle to the transformer on the ground) and a long ladder (allowing maintenance personnel to reach the nacelle).
Because wind turbines evolved from wind engines, they are all generally built with self-luffing technology to keep the sails facing the wind. On smaller systems, this means a simple vane attached to the gearbox. On utility turbines, gearbox and luffing equipment is house within the nacelle—the equivalent of a cap on a custom windmill. Because it rests on a live curb ring, the nacelle can pivot 360 degrees in the event the wind changes direction (see Wind Turbine Operation).
The nacelle is usually constructed in the form of a rectangular prism and made of steel. The nacelle must be built strong enough to accommodate the gears and large electrical components within. Many nacelles open with a hinged hood—almost like a giant toolbox—so that the major components can easily be installed or replaced over time. The exterior of the nacelle doubles as advertising space for manufacturers to display their logo.
Shown below are the various sail designs employed to generate electricity. The first wind turbines were designed from annular-sailed wind engines. Over the years, both individuals and companies have experimented with sail design for both horizontal and vertical axis turbines.
The sails of a wind turbine are unlike those of any other wind machine. The large, fiberglass sails of utility turbines are specially shaped and tested to turn in light winds and withstand strong gales. The sails can be pivoted upon their own axis to expose more or less surface area to the wind, depending on the speed.
Wind Farm Development and Assembly
Long before wind turbines (or wind farms) are built, field tests are performed on areas where turbines may be built. These tests measure the speed and direction of the wind at varying heights to determine whether there is sufficient wind to sustain a turbine. More wind turbines are located in rural areas or along a coast because the wind is constant and there are fewer obstructions. This data is often collected by an anemometer, a device with cup-like “sails” rotating upon a vertical axis.
Other factors, such as temperature fluctuation, ground conditions, interference from surroundings, and anticipated energy usage are also considered when choosing a turbine style and location. In the Midwest, turbines are made of fiberglass that can withstand seasonal temperature changes and fierce winds from severe storms.
Once an area is deemed suitable for turbine construction, planners meet with government agencies at the local and state levels seeking permits to allow construction. Public hearings are held so that landowners may offer their opinions about the project. If approved, surveyors will identify where turbine towers, transformers, electric lines, and service roads will be.
Engineers work at manufacturing the turbines and design how to integrate a wind farm with the existing power grid. Meanwhile, the turbine sails, tower, and nacelle are manufactured at their respective plants, oftentimes overseas. The tower and nacelle are constructed in [large] pieces to be assembled later; the sails, however, must be cast as a single, continuous piece of fiberglass.
To make turbines compatible with the local power grid, the electrical components are usually made in the United States. The generator and ground equipment that will regulate both turbine operation and the flow of electricity
Once the pieces of each turbine are completed, they are shipped to the United States by barge. In the early 2000s when wind turbine construction began increasing, receiving docks at ports had to be equipped with special handling equipment to unload the large sails.
The turbine pieces are then transported by train and truck to a distribution warehouse. There, the turbine pieces, fasteners, electrical components, cables, and tools are stored and partially assembled until construction can begin. During this time, technicians will be hired and trained to maintain the turbines.
Gravel service roads are laid out on the land so that heavy construction equipment can reach each turbine site. Earth boring machines create the deep holes that will be filled with concrete to create the footings of each tower. When the concrete cures, underground cables and utility boxes are installed that will regulate the turbine; these lines will run to a central control center for the entire wind farm facility.
The tower is constructed in sections, each held together by large stainless steel bolts. The electrical equipment is installed in the nacelle, which is then lifted onto the tower with a large crane. Each of the three sails is attached to the hub on the ground, and then the entire assembly is lifted and bolted into place. Once all of the components are attached and thoroughly tested, operation of the turbine can begin.
One of the Mendota Hills turbines.
Photo by Tom Haskell
Crews work on the nacelle prior to sail installation.
Photo from Suzlon Wind Energy
Sail detail of "Big Windy" at the Great Escape Restaurant in Schiller Park.
Photo by Tom Haskell
Pieces of each turbine tower are lifted into place using a large crane. The sails are installed last.
Illustration by Tom Haskell